1. Field of the Invention
The present invention relates to a sheet-feed device configured such that recording sheets stacked on a sheet accommodating portion are separated one by one by a sheet-feed roller or rollers and a plurality of separation pawls, for feeding the separated one of the recording sheets. The invention also relates to the image recording apparatus having an image recording unit for recording an image on the separated one of the recording sheets fed by the sheet-feed device.
2. Discussion of Related Art
An image recording apparatus, such as a printer, a copying machine, a facsimile machine or the like, is generally equipped with a sheet-feed device that separates cut sheets (i.e., recording sheets each as a recording medium) one by one and feeds the separated sheet to an image recording unit of the image recording apparatus.
For instance, Patent Document 1 (U.S. Patent Application Publication No. US 2006/0180992 A1 corresponding to JP-A-2006-182481) discloses a sheet-feed device provided on an image recording apparatus. The disclosed sheet-feed device includes: a sheet-supply cassette, as a sheet accommodating portion, opening upward and accommodating a stack of recording sheets; and a sheet-feed roller provided at a distal end of an arm which is disposed above the sheet-supply cassette so as to be pivotable upward and downward. The sheet-supply cassette includes: an inclined sheet-separation plate disposed at its downstream end portion in a sheet-feed direction in which the recording sheets are fed; and a sheet-separation member disposed at a middle portion of the inclined sheet-separation plate in its width direction, i.e., in a width direction of the recording sheets.
The sheet-separation member disclosed in the Patent Document 1 includes: a metal base portion; pawl-like separation protrusions; arm portions each of which supports a corresponding one of the separation protrusions at opposite sides thereof; and leaf spring portions which are formed integrally with the base portion and by which the sheet-separation member is fixed to a prescribed position on a rear surface of the inclined sheet-separation plate. The separation protrusions, the arm portions, and the leaf spring portions are formed on the base portion by press working so as to be arranged in the sheet-feed direction at suitable intervals. Each of the separation protrusions is configured to protrude, by a suitable amount, in a direction in which the separation protrusion is to contact the recording sheet being fed in the sheet-feed direction. Each separation protrusion protrudes through a corresponding one of windows formed in the inclined sheet-separation plate so as to be arranged in the sheet-feed direction.
In the sheet-feed device disclosed in the Patent Document 1, the sheet-feed roller is rotatably driven while pressing an uppermost one of the recording sheets stacked in the sheet-supply cassette, whereby the recording sheets accommodated in the sheet-supply cassette are fed one by one. Since the sheet-feed roller is disposed so as to swing upward and downward, a pressing force with which the sheet-feed roller presses the recording sheets accommodated in the sheet-supply cassette varies depending on a vertical position of the sheet-feed roller, i.e., depending on the amount of the recording sheets stacked in the sheet-supply cassette. In the thus constructed sheet-feed device, where the pressing force of the sheet-feed roller with which the sheet-feed roller presses the recording sheets is large, there may be a risk of so-called multi-feeding, namely, a risk that two or more of the recording sheets are fed at one time in an overlapping state, from the stack of the recording sheets accommodated in the sheet-supply cassette.
In this respect, where two or more of the recording sheets are fed at one time in the sheet-feed device disclosed in the Patent Document 1, leading edges of the respective two or more of the recording sheets come into contact with the separation protrusions provided on the inclined sheet-separation plate, so that the two or more of the sheets being fed in the overlapping state are separated from one another, namely one by one, by a cooperative action of the sheet-feed roller and the separation protrusions. Thus, the above-indicated multi-feeding is prevented in the sheet-feed device disclosed in the Patent Document 1.
The thus separated one of the recording sheets by the cooperative action of the sheet-feed roller and the separation protrusions is fed to the image recording unit disposed above the sheet-supply cassette via a sheet-feed path having a U-turned portion that is provided above the inclined sheet-separation plate, so that an image is recorded on the one of the recording sheets by the image recording unit, and the sheet is consequently discharged through a sheet-discharge portion.
In the thus constructed sheet-feed device disclosed in the Patent Document 1, each of the recording sheets accommodated in the sheet-supply cassette reaches the image recording unit through the sheet-feed path, and the image recording unit records an image on the recording sheet from above the recording sheet. Accordingly, the recording surface of each of the recording sheets on which an image is to be recorded by the image recording unit faces downward in a state in which the recording sheets are accommodated in the sheet-supply cassette. During feeding of each of the recording sheets through the U-turned portion of the sheet-feed path, the recording sheet is turned upside down, so that the recording surface of the recording sheet faces upward.
Before the recording sheet passes through the U-turned portion of the sheet-feed path, the recording sheet is fed on the inclined sheet-separation plate while facing the separation protrusions that are provided on the inclined sheet-separation plate. As described above, since the direction of feeding of each recording sheet is changed during the recording sheet passes through the U-turned path portion whose radius of curvature is small, it is likely that the recording surface of the recording sheet being fed comes into strong contact with the separation protrusions. In this instance, the sheet recording surface may surfer from scratches or damages due to the strong contact with the separation protrusions, undesirably causing a problem that the quality of the image to be recorded on the damaged recording surface is deteriorated.
The above-described problem is serious particularly when a glossy paper which has a larger thickness and is more unlikely to bend, than a plain paper (such as a copy paper), is used. The glossy paper is used exclusively for recording photographic data with use of a large amount of ink and includes a base layer and a coating layer which is superposed on the base layer for adjusting absorption of ink, for instance. One of opposite surfaces of the glossy paper on which the coating layer is formed functions as the recording surface.
Where the glossy paper is used as the recording medium in the sheet-feed device constructed as described above, there may be a possibility that the coating layer on the recording surface comes into contact with the separation protrusions. As mentioned above, the glossy paper has a lager thickness and is more unlikely to bend, than the plain paper. Accordingly, the glossy paper tends to strongly contact the separation protrusions. In other words, where the glossy paper is used as the recording medium, the coating layer on the recording surface may be seriously damaged, resulting in a considerable difference in the image quality between the damaged portion of the recording surface and the other portion of the recording surface. Because the use of the glossy paper has the great advantage of providing or assuring excellent image quality, the deterioration in the image quality due to the damage of the coating layer by the contact with the separation protrusions is quite serious.
In this regard, the sheet-feed device disclosed in the above-indicated Patent Document 1 is configured such that the height, i.e., the amount of protrusion, of one of the separation protrusions located on the most downstream side in the sheet-feed direction is made smaller than that of the other separation protrusions located on the upstream side, thereby reducing the damage of the sheet recording surface.